Airbag gas producer

ABSTRACT

A gas generator for an air bag comprises: a housing having a gas discharging port; an initiator assembly provided with a first igniter and a second igniter mounted to the housing via a holder, each of the first igniter and the second igniter including a priming activated upon an impact, the second igniter having, a center pin connected to an external power supply to constitute a positive electrode, a grounding pin connected to a metal portion of a motor vehicle to constitute a negative electrode, and an opening-shutting device of current provided between the center pin and the external power supply; and gas generating material ignited and burnt by the initiator assembly.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP01/05321 which has an Internationalfiling date of Jun. 21, 2001, which designated the United States ofAmerica.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas generator for an air bag and anair bag system using the same.

2. Description of Related Art

As a gas generator for an air bag, there are a pyrotechnic-type gasgenerator in which only a gas generated by combustion of a gasgenerating agent is used for inflating an air bag, and a hybrid-type gasgenerator in which a gas generated by combustion of a gas generatingagent and a pressurized medium are used for inflating the air bag. Inthe gas generator for the air bag, ignition means provided with anigniter is employed as means for generating a gas by combusting the gasgenerating agent, and a single-type gas generator with one igniter and adual-type gas generator with two igniters are used at present.

In the case of a dual-type gas generator with two igniters, twoconductive pins (a center pin and a grounding pin) of the positiveelectrode and the negative electrode are provided in the respectiveigniters. By electrifying the respective conductive pins, a priming isignited and burnt at conductive wires (namely, heat generating wires,electric resistance wires or the like), which connect the two conductivepins, in the course of current flows from the positive electrodes to thenegative electrodes and the gas generating agents are burnt, in somecases, through ignition and burning of transfer charges.

As such a dual type gas generator for the air bag, there is one which isadjusted to activate only one igniter or to activate both ignitersaccording to the magnitude of an impact on the vehicle. In this case, itis important that the other igniter is not activated erroneously whenthe magnitude of impact is relatively small and only one igniter isactuated.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a gas generator for anair bag in which an erroneous activation of a second igniter due to anactuation of a first igniter can be prevented with increasedreliability, and an air bag system using the same.

As a solution, the present invention provides a gas generator for an airbag which comprises, a housing having a gas discharging port, aninitiator assembly provided with first and second igniters mounted tothe housing via a holder, each of the first and second ignitersincluding a priming activated upon an impact,

-   -   the second igniter having,        -   a center pin connected to an external power supply to            constitute a positive electrode,        -   a grounding pin connected to a metal portion of a motor            vehicle to constitute a negative electrode, and        -   opening-shutting means of current provided between the            center pin and the external power supply; and    -   gas generating means ignited and burned by the initiator        assembly.

The second igniter constituting the ignition means can be adjusted to beactivated simultaneously with the first igniter or to be activated afterthe first igniter is activated.

In this invention, the grounding pin and the center pin are connected toeach other by a conductive wire (that is, a heat generating wire, anelectric resistance wire or the like) at positions where one end portionof each pin makes contact with the priming, and the priming is ignitedand burnt by electrifying the conductive wire. Furthermore, thegrounding pin is a conductive pin that makes contact with a conductivebody (for example, a metallic eyelet), and the center pin is aconductive pin insulated from the conductive wire by glass or the like.Incidentally, the conductive pin serving as the negative electrode isconnected to a metal portion of a vehicle to ground. For example, thegrounding pin may be electrically connected to a metal portionconstituting an outer shell vessel of the igniter, and the center pinmay be electrically connected to the grounding pin only via an electricresistance wire. Here, electrical connection means is connected to thepins directly or indirectly via another conductive member.

In the gas generator for an air bag of the present invention, the centerpin of the second igniter is set to the positive electrode and thegrounding pin is set to the negative electrode. Accordingly, when (+)current flows from the first igniter to the conductive member (themetallic eyelet), the (+) current flows to the grounding pin of thenegative electrode to be discharged due to grounding, and thereby thesecond igniter can never be activated erroneously.

Further, the gas generator for an air bag of the present invention isprovided with opening-shutting means for selectively allowing orpreventing current from flowing to the center pin of the second igniterfrom the external power supply. In case that only the first igniter isactivated, the opening-shutting means is open and current does not flowinto the center pin, so that current is prevented from flowing from thecenter pin of the second igniter to the negative electrode of the firstigniter via the conductive wire (that is, a heat generating wire, anelectric resistance wire or the like). Accordingly, the second ignitercan never be activated erroneously.

Since the gas generator for an air bag of the present invention isarranged such that the positive electrode and the negative electrode ofthe conductive pins are arranged as described above in the two igniters,and due the opening-shutting means of current, the present invention isnot particularly limited to the structure of the gas generator for anair bag itself, but, for example, the ignition means can be constitutedas the following initiator assembly.

In the present invention, the initiator assembly may further include atransfer charge,

-   -   a collar assembly retaining the initiator assembly to the gas        generator, and    -   preferably, the collar assembly has an insulating material        surrounding at least a portion of each of the first and second        igniters and a collar joined to the insulating material.

Incidentally, the collar forming the collar assembly, that is, a holder,may be any member having a function serving as a collar (a spaceretaining function), and preferably it is made of ceramics or metal;more preferably, it is made of metal.

Further, preferably, at least one of the first and second ignitersincludes, a metallic eyelet having a hole through which one of thecenter pin and the grounding pin passes, and an electrically insulatingbody filled in the hole to insulate the conductive pin from the eyeletare provided such that the end faces thereof exist on the same plane.

Next, a preferable initiator assembly used in the gas generator for anair bag of the present invention will be explained.

When the initiator assembly is activated by an ignition signal receivedby the conductive pin of the initiator, it ignites and burns the primingdisposed in the vicinity of the conductive pin. The initiator assemblyincludes the first and second igniters, and the collar assembly joinedthereto. In addition to the at least one conductive pin, the first andsecond igniters each have a charge holder formed by using a cap member(cover member) comprising a metallic wall or a resin surrounding thepriming ignited when an ignition signal is received. The collar memberretains the initiator assembly to the housing of the inflator even afterthe initiator assembly is activated.

The collar assembly includes an injection-molded insulating material anda collar, and the collar is fixed and joined to the insulating materialmade of an injection-molding plastic material during aninjection-molding process.

The insulating material is useful for insulating one conductive pin fromthe second conductive pin, or in another embodiment, it is useful forinsulating one conductive pin from another conductive component in adifferent electric potential therefrom when the one conductive pinreceives an ignition signal.

The collar is a single integral piece which can be defined to include abody portion and a shoulder portion. The body portion is arranged sothat a front end annular cylindrical portion thereof is fitted and fixedon the outer periphery of the insulating material made of a moldingplastic material injection-molded to surround conductive pins, generallytwo conductive pins comprising the center pin and the grounding pin. Theconductive pins extend inside a cylindrical portion extending rearward.Then, the inner space of the rearward cylindrical body receives aconnector connected to the conductive pins. In this collar, it ispreferable that the inner circumferential surface of the cylindricalbody portion extending rearward (that is, a rear half) is formed not tobe covered with an insulating material (that is, injection-molded resinor the like), exposing the collar. This is for securely eliminating apossibility such that a connector disposed in the inner space of thecylindrical portion drops off due to, for example, the impact ofactivation of the first and second igniters.

The shoulder portion is expanded outwardly in the radial direction fromthe rearward cylindrical portion of the body portion to becontact-engaged with an engaging portion of the housing of the inflator.The mutual engagement between the shoulder portion and the engagingportion of the inflator housing controls the relative positioning of theinitiator assembly to the inflator housing before and after activationof the initiator assembly. The outward position of the shoulder portiondefines the length or the dimension of the outside of the collar.

In the initiator assembly of this invention, the priming is stored in acharge holder made of a cover member comprising a cylindrical metallicwall, a resin or the like mounted to a metallic eyelet (end plate), themetallic eyelet has a cylindrical shape with a hole, and the hole formedin a center of the eyelet is filled with an electrical insulator(comprising glass).

The center pin of the electrode extends through the insulating materialin the collar, then goes through a electrical insulating body in theeyelet, and the front end thereof makes contact with the priming. Also,the upper surface of the eyelet also makes contact with the priming, andthe front end of the second conductive pin, namely the grounding pin ofthe electrode is connected to the lower surface of the eyelet in a stateof being able to be electrified. As the priming stored in the covermember or the charge holder, a material of zirconium-potassiumperchlorate can be used. A means for igniting the priming on the basisof an ignition signal is provided between the center pin described aboveand the eyelet. That is, the means comprises a resistance wire connectedbetween the both. The initiator assembly used in the present inventionhas the following features.

(1) The end surfaces of the center pin, the eyelet, and the electricalinsulating material are on the same plane, and they are integrally fixedby molding a resin together with the collar, thereby forming a pin-type.The pin-type is an igniter in which the conductive pins project in thecollar assembly, particularly, in the inner space of the rearwardcylindrical body of the body portion in the collar, and the conductivepins and lead wires are connected by receiving and engaging theconnector at the front ends of lead wires in the inner space of therearward cylindrical body in the body portion, and thereby the both aremade conductive. Such a pin-type aims to downsize the initiator and makethe initiator handy by attaching the connector and the lead wiresseparately afterwards. In such a pin-type, by positioning the endsurfaces of the center pin, the eyelet and the insulating body on thesame plane, the initiator assembly which is easily manufactured and inthat a manufacturing cost is not increased is realized.

That is, the igniter activated by an electric signal needs to have astructure for igniting and burning the priming by an electricalactivation signal, and an electric resistance body (resistance wires inthe present specification) for converting electric energy (that is, anelectric signal) to heat energy is used as such a structure. Theresistance wires are provided to connect one conductive pin and anotherconductive component (for example, another conductive pin or an eyelet)having a different electrical potential therefrom when the oneconductive pin receives the ignition signal, and preferably at thistime, the resistance wire is provided straight without sagging betweenthe conductive pin and the conductive component. If the end surfaces ofthe center pin, the eyelet and the insulating body are on the sameplane, by pulling and welding the resistance wires to the conductive pinand the conductive component, the resistance wires can be arranged toabut the flat end surfaces of the center pin, the eyelet and theinsulating body without sagging. That is, the resistance wires can beconnected to the conductive pin and the conductive component easily andsecurely.

(2) As the insulating material surrounding a portion of the initiator, aplastic material which can be injection-molded is used. As such a resin,nylon 6/12 resin, polybutylene terephthalate (PBT) resin, or polyacetalresin is used. By using these resins, the insulating resistance isincreased as compared with nylon 6 resin which has been usedconventionally, so that insulation between the conductive pins andbetween the conductive pins and the collar can be obtained securely.

(3) In order to increase friction between the inner cylindrical memberof the inflator and the initiator assembly, and prevent rattling orrotation of the initiator assembly so that a crimping process of theinner cylindrical member is facilitated, a projection is formed on theouter periphery of the insulating material (molded resin portion)surrounding the metallic eyelet (end plate). It is preferable that theprojection is formed in one of various cone shapes such as a circularcone, a pyramid or the like, but even another shape can be employed aslong as it can be fitted in between the inner cylindrical member and theinitiator assembly to increase the frictional resistance therebetween.Also, the projection is formed to have a size slightly larger than a gapobtained between the inner cylindrical member and the initiatorassembly, and it is formed to be collapsed or flexed and press-fittedbetween the initiator assembly and the inner cylindrical member, whenthe initiator assembly is joined to one end of the inner cylindricalmember. In order to secure such a function, for example, when the widthof the gap is 0.75 mm, the function can be realized by forming theprojection in a size larger than the gap by 0.1 to 0.2 mm or so.

(4) The center pin and the grounding pin in the connecting space withthe connector in the collar are arranged such that they do not projectout of the collar in order to prevent the pins from deforming duringassembling the initiator assembly.

(5) Connector dropping-out preventing means is provided in theconnecting space with the connector in the collar. For this, it issufficient to provide a recessed notch inside the collar.

(6) In order to coincide the conductive pins (the grounding pin and thecenter pin) and the connector with each other regarding positive andnegative electrodes, a D feature type or T feature type projection isprovided in the connecting space. More particularly, a projection orrecess in a D-letter or T-letter shape is formed on the insulatingmaterial (molded resin) exposing to the bottom surface of the connectorconnecting space.

(7) The inside of the collar is not covered with the injection-moldedinsulating material (molding plastic material), and the connector isfitted to make contact directly with the metal surface of the inside ofthe collar. Thereby, the connector can be prevented from falling out dueto the reaction of activation of the igniter.

(8) Mounting means for a connector having lead wires is provided todirect the lead wires towards a predetermined direction with respect tothe gas generator. Specifically, recesses or projections extending inthe axial direction are provided on an edge portion of the collar inasymmetrical manner.

The gas generator for an air bag of the present invention may have astructure such that an air bag is inflated by only a combustion gasgenerated by combustion of the gas generating means.

Also, the present invention provides an air bag system including a gasgenerator for an air bag, an impact sensor for detecting an impact toactivate the gas generator, an air bag introduced therein a gasgenerated in the gas generator and/or a pressurized medium to inflate,wherein the gas generator for an air bag is the gas generator for an airbag described above.

Particularly, the air bag system in the present invention can beprovided with the following structure.

That is, an air bag system is an air bag apparatus comprising a gasgenerator for an air bag accommodating ignition means in a housinghaving a gas discharging port and an activation-signal outputting devicefor outputting an electrical-activation signal to the gas generator,wherein the ignition means is provided with a first igniter and a secondigniter activated by the electrical activation-signal and the first andsecond igniters are mounted to the housing via a holder, the ignitercomprises a grounding pin electrically connected to a metal portion ofan outer shell in the igniter and a center pin electrically connected tothe grounding pin via only an electric resistance wire, and theactivation-signal outputting device is provided with an opening-shuttingmeans controlling the output of the activation-signal to each igniter,and in the second igniter, the center pin is connected toactivation-signal outputting means to serve as the positive electrode.

The activation-signal outputting means described above is a device whichcan output an electrical activation-signal to at least the igniter, andone provided as a control unit conventionally or one provided by beingcombined with the control unit and an impact sensor or the like can beused as such means.

The present invention also provides a method of receiving anactivation-signal in a gas generator for an air bag activated byreceiving an electrical activation-signal.

That is, in the method of receiving an activation-signal, a gasgenerator comprises ignition means in a housing having a gas dischargingport, the ignition means is provided with a first igniter and a secondigniter activated by an electrical activation-signal, the first andsecond igniters are mounted to the housing via a holder, and the ignitercomprises a grounding pin electrically connected to a metal portion ofan outer shell of the igniter and a center pin electrically connected tothe grounding pin via only an electric resistance wire, and in thesecond igniter, the center pin serves as the positive electrode toreceive the electric activation-signal.

In the gas generator for an air bag of the present invention, there isno possibility that the second igniter may be activated erroneously byactivation of the first igniter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view of a gas generator for an airbag of one embodiment of the present invention;

FIG. 2 is a vertical cross sectional view of ignition means shown inFIG. 1;

FIG. 3 is a cross sectional view for explaining the structure of theignition means;

FIG. 4 is a vertical cross sectional view of a gas generator for an airbag of another embodiment of the present invention;

FIG. 5 is a cross sectional view of ignition means shown in FIG. 4; and

FIG. 6 is a schematic view showing an embodiment of an air bag system ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of a gas generator for an air bag of the presentinvention will be explained with reference to FIG. 1 to FIG. 3. FIG. 1is a vertical cross sectional view of a gas generator for an air bag,FIG. 2 is a vertical cross sectional view of an igniter shown in FIG. 1,and FIG. 3 is a cross sectional view for explaining an inner structureof the igniter. FIG. 1 shows a pyrotechnic type gas generator for an airbag in which only a gas generated by combustion of a gas generatingagent inflates an air bag.

In the gas generator shown in FIG. 1, a substantiallycylindrically-shaped inner cylindrical member 104 is arranged in ahousing 103 formed by joining a diffuser shell 101, having a gasdischarging port, and a closure shell 102 forming an inner accommodatingspace together with the diffuser shell. The inner accommodating spaceoutside the inner cylindrical member 104 is a first combustion chamber105 a.

A stepped notch portion is provided inside the inner cylindrical member104 receives a disk-like partition wall 107. A space in the innercylindrical member 104 is partitioned into two chambers by the partitionwall 107 such that a second combustion chamber 105 b is defined in thediffuser shell side (the upper space) and a space for accommodatingignition means is defined in the closure shell side (the lower space).

Gas generating agents 109 a and 109 b, which are burnt by the ignitionmeans activated due to an impact to generate a combustion gas, arestored in the first and second combustion chambers 105 a and 105 b, andthe ignition means is provided with a first igniter 112 a and a secondigniter 112 b which are activated due to the impact for ignition.

The first igniter 112 a and the second igniter 112 b are activated by anactivation-signal output on the basis of a sensor detecting an impact,and they are provided in parallel in an initiator collar 113 serving asa holder, having their head portions exposed. The first igniter 112 aand the second igniter 112 b are fixed to the initiator collar 113 by ametallic pressing member 130 from the above.

As shown in FIG. 2, the first igniter 112 a has a grounding pin 181 (anegative electrode (or a positive electrode)) and a center pin 182 (apositive electrode (or the negative electrode)). One end of thegrounding pin 181 and the center pin 182 are connected electrically toeach other by a bridge wire 119 which is a conductive wire such as anelectric resistance wire or the like at the portions thereof in contactwith a priming 197 as shown in FIG. 3. The other end of the groundingpin 181 is connected to a metal portion of a motor vehicle via aconnector to ground, while the other end of the center pin 182 isconnected to an external power supply via the connector. Furthermore, apart of the grounding pin 181 is connected to a metallic eyelet 195; andthe center pin 182 is insulated from the metallic eyelet 195 by a glass196. A bridge wire (an electric resistance wire) 119 is connectedbetween the one end of the center pin 182 and the one end of the eyelet,and the bridge wire 119 is in contact with a priming 197. Thereby, whenthe center pin 182 is electrified, current flows through the bridge wire119 so that the priming 197 is ignited. Further, the first igniter 112 ahas a structure such that the priming 197 and a charge holder 121 aredisposed inside a metallic cover member 164. The cover member 164 andthe eyelet 195 make contact with each other. The cover member 164 can becovered with a thin film to provide electrical insulation.

The second igniter 112 b has a grounding pin 191 (a negative electrode)and a center pin 192 (a positive electrode). One end of the groundingpin 191 via the eyelet 195 and one end of the center pin 192 areconnected to each other by a bridge wire 119, which is a conductive wiresuch as an electric resistance wire or the like, at the portions thereofin contact with a priming 197. The other end of the grounding pin 191 isconnected to a metal portion of the motor vehicle via a connector toground, while the other end of the center pin 192 is connected to anexternal power supply via the connector. Opening-shutting means (aswitch) of current (not shown) is provided between the center pin 192and the external power supply. Furthermore, a part of the grounding pin191 is connected to a metallic eyelet 195, and the center pin 192 isinsulated from the metallic eyelet 195 by a glass 196. A bridge wire(electric resistance wire) 119 is connected between the one end of thecenter pin 192 and the eyelet 195, which is electrically connected tothe grounding pin 191, and the bridge wire 119 is in contact with apriming 197. Thereby, when the center pin 192 is electrified, currentflows through the bridge wire 119 so that the priming 197 is ignited.Further, the second igniter 112 b has a structure such that the priming197 and a charge holder 121 are disposed inside a metallic cover member164, and the cover member 164 and the eyelet 195 make contact with eachother. Also, the cover member 164 can be covered with a thin film toprovide electrical insulation.

A transfer charge 116 accommodated in an aluminum cup is disposed abovethe first igniter 112 a, and the transfer charge 116 is separated fromthe second combustion chamber 105 b by a substantially cylindricalpartition member 140 and the partition wall 107. A flame-transferringhole 117 is provided in the inner cylindrical member 104, and the hole117 is closed by a seal tape 118.

A through-hole 110 is provided in the inner cylindrical member 104defining the first combustion chamber 105 a and the second combustionchamber 105 b, and the through-hole is closed by a seal tape 111.Incidentally, since the seal tape 111 is ruptured when the gasgenerating agent is burnt, both the combustion chambers can communicatewith each other through the through-hole 110. An opening area of thethrough-hole 110 is larger than that of the gas discharging port 126,and it does not have a function for controlling the internal pressure inthe second combustion chamber 105 b.

A common coolant-filter 122 for purifying and cooling combustion gasesgenerated by combustion of the first and second gas generating agents109 a and 109 b is disposed in the housing 103, and an innercircumferential surface of the filter 122 in the diffuser shell 101 sideis covered with a short-pass preventing member 123.

Outside the coolant-filter 122, an outer layer 124 for suppressingexpansion of the filter 122 due to passing of the combustion gas or thelike is disposed. The outer layer 124 can be made of, for example, alaminated wire mesh body.

A gap 125 is formed outside the outer layer 124 such that the combustiongas can pass through all portions of the filter 122. A gas dischargingport 126 formed in the diffuser shell is closed by a seal tape 127 inorder to block the outside air.

When the center pin 182 of the first igniter 112 a is electrified,current flows into the grounding pin 181 via the bridge wire 119, thepriming 197 is ignited and burnt in the course, and then the transfercharge 116 is ignited and burnt. Then, the seal tape 118 is ruptured bya high-temperature gas generated by combustion of the transfer charge116. The high temperature gas flows through the flame-transferring hole117 into the first combustion chamber 105 a to ignite the first gasgenerating agent 109 a, and thereby a gas is generated.

In this case, when the priming 197 is ignited and burnt by activation ofthe first igniter 112 a, the metallic pressing member 130 may break by apressure of that combustion and the broken portion may make a bridgebetween the first igniter 112 a and the second igniter 112 b. In such asituation, (+) current can flow in the second igniter 112 b via thepressing member 130, or the pressing member 130 and the partition member140.

Also, in a case that the metallic cover member 164 accommodating thepriming 197 in the first igniter 112 a makes contact with the pressingmember 130 to be electrified due to activation of the first igniter 112a, broken portions of the cover member 164 and the pressing member 130may make a bridge between the first igniter 112 a and the second igniter112 b. In such a situation, (+) current of the first igniter 112 a canflow into the second igniter 112 b via the pressing member 130, or thepressing member 130 and the partition member 140. At this time, evenwhen an outer surface of the cover member 164 in both igniters iscovered with a film having an insulation property (hereinafter, referredto as an insulating film), the same problem occurs when the film isbroken.

Then, regarding the possibility that (+) current of the first igniter112 a flows into the second igniter 112 b, even if the center pin in thefirst igniter 112 a is set to (+) pole, a similar problem will occurwhen a tip end portion of the bridge wire connected to the center pin182 makes contact with a conductive portion such as the cover member 164or the like, for any reason, after activation of the first igniter 112a.

However, in the case that (+) current flows in the second igniter 112 bin this manner, the (+) current flows in only the grounding pin 191, andit never flows in the center pin 192.

Furthermore, when only the first igniter 112 a is activated, theopening-shutting means of current between the center pin 192 of thesecond igniter 112 b and the external power supply is open so thatcurrent never flows in the center pin 192. In a case that theopening-shutting means is shut or there is no opening-shutting means,(+) current flows from the center pin 192 to the grounding pin 181 ofthe first igniter 112 a through the bridge wire 119 and the bridgingbroken portion. In that course, the priming 197 is ignited so that thesecond igniter 112 b may be activated erroneously.

As mentioned above, in the present invention, since the center pin 192of the second igniter 112 b is set to the positive electrode and theopening-shutting means of current is provided between the center pin 192and the external power supply, an erroneous activity of the secondigniter 112 b can be prevented unfailingly.

Next, another embodiment of the gas generator for an air bag of thepresent invention will be explained with reference to FIG. 4 and FIG. 5.FIG. 4 is a vertical cross sectional view of a gas generator for an airbag according to another embodiment of the present invention, and FIG. 5is a vertical cross sectional view of the initiator assembly shown inFIG. 4. FIG. 4 shows a pyrotechnic type gas generator for an air bag inwhich only a gas generated by combustion of a gas generating agentinflates an air bag. This gas generator is different in ignition meansfrom the gas generator for an air bag shown in FIG. 1, but isapproximately identical in other portions, so that only the ignitionmeans will be explained.

The ignition means includes an initiator assembly 10 and a transfercharge 116 filled in an aluminum cup. The initiator assembly 10 isfitted into an inner cylindrical member 104 (in the space formed by theinner cylindrical member 104 and the partition wall 107), and it ismounted thereto by crimping a lower end portion 104 a of the innercylindrical member 104.

The initiator assembly 10 includes a first igniter 23 a, a secondigniter 23 b and a collar assembly 31.

The collar assembly 31 includes a resin portion 36 made of a moldingplastic material as a injection-molded insulating material and ametallic collar 40, and the base portions of the first igniter 32 a andthe second igniter 32 b are surrounded by the resin portion 36.

The metallic collar 40 is joined to the resin portion 36. For joiningthe collar assembly 31 comprising the resin portion 36 and the metalliccollar 40 integrally with the first igniter 32 a and the second igniter32 b, an injection-molding process is employed. In this case,liquid-like or fluidized molding plastic material constituting the resinportion 36 is filled between the base portions of the first igniter 32 aand the second igniter 32 b and the metallic collar 40. When the plasticmaterial is solidified, the metallic collar 40 is fixed to and retainedto the resin portion 36, and the resin portion 36 is fixed on andretained to the first igniter 32 a and the second igniter 32 b.

A groove 202 is formed around a lower end portion of the metallic collar40 of the initiator assembly 10, and an O-ring made of rubber, plasticor the like is fitted in the groove 202. Then, by arranging the O-ring200 in this manner, moisture is prevented from entering from thecontacting portion between the inner cylindrical member 104 and theinitiator assembly 10 (metallic collar 40), so that the interior of thegas generator for an air bag is kept in a moisture-proof state. Thus,since the interior is kept in the moisture-proof state, the performanceof the gas generating agents 109 a and 109 b is prevented fromdeteriorating due to moisture absorption. Furthermore, although theinitiator assembly 10 includes the first initiator 32 a and the secondinitiator 32 b, it is necessary to provide only one O-ring 200.Therefore, the number of manufacturing steps for the initiator assembly10 is not increased as compared with that for a gas generator having asingle initiator, and moisture-proof of the former is substantiallyequal to that of the latter.

The first igniter 32 a and the second igniter 32 b include a metalliceyelet (end plate) 46 in which a hole 50 is formed. The first igniter 32a has a center pin 54 a (the positive electrode (or the negativeelectrode)) and a grounding pin 70 a (the negative electrode (or thepositive electrode)), while the second igniter 32 b has a center pin 54b (the positive electrode) and a grounding pin 70 b (the negativeelectrode). Then, an unillustrated opening-shutting means of current isprovided between the center pin 54 b and an external power supply. Then,in the both igniters, bridge wires which are conductive wires, such aselectric resistance wires, are disposed respectively between the centerpins 54 a and 54 b and the eyelets 46, and are in contact with thepriming 62. When current flows in the center pins 54 a and 54 b, thebridge wires generate heat to ignite the priming 62. Also, the covermember 64 may be covered with a thin film to provide an electricalinsulation.

The upper portions of the center pins 54 a and 54 b go through holes 50,and the center pins 54 a and 54 b are positioned, insulated against themetallic eyelets 46 by glasses 33 corresponding to an electricalinsulating body.

The center pins 54 a and 54 b transmit ignition signals for igniting thepriming 62. The cover member 64 comprising a metal wall encloses orcovers the priming 62 filled in the charge holder 21 and it is welded tothe eyelet 46. It is preferable that a circular end portion of the covermember 64 is provided with notches so that it can be broken easily andunfailingly. Such notches can be formed as grooves of about 0.10 to 0.25mm radially, in case that the cover member 64 is made of stainless steel(SUS305).

The grounding pins 70 a and 70 b are insulated from the center pins 54 aand 54 b, respectively, by glasses 33.

The resin portion 36 made of molding plastic material surrounds themetallic eyelets 46 of the first igniter 32 a and the second igniter 32b, the center pins 54 a, 54 b and the grounding pins 70 a, 70 b, and inaddition, the metallic collar 40 is mounted to the outside of the resinportion 36.

The resin portion 36 is resin-molded integrally, including the metalliccollar 40. At this time, the end surfaces of the center pins 54 a and 54b, the eyelets 46, the glasses 33 holding the center pins 54 a and 54 bin the holes 50 of the eyelets 46 are put on the same plane.

Also, a front end peripheral surface of the resin portion 36 and a frontend peripheral surface of the metallic collar 40 surrounding the resinportion 36 form a continuous circumferential surface to be frictionallyfitted into the inner cylindrical member 104 shown in FIG. 4, and aprojection 42 is formed on a front end peripheral surface of the resinportion 36. The projection 42 increases the friction between the innercylindrical member 104 and the initiator assembly 10, prevents rattlingor rotation of the initiator assembly 10, and facilitates a crimpingprocess of the inner cylindrical member 104.

The base portion of the resin portion 36, through which the center pins54 a, 54 b and the grounding pins 70 a, 70 b pass, insulates themetallic collar 40 from the center pins 54 a, 54 b and the groundingpins 70 a, 70 b. The metallic collar 40 has cavities 85 inside, and asurface of the cavity 85 is not covered with the molding plasticmaterial and the metallic collar is exposed.

The tip end portions of the center pins 54 a, 54 b and the groundingpins 70 a, 70 b protrude in the cavities 85 but the tip end portions arenot exposed out of the cavities 85 of the metallic collars 40. This isfor preventing the pins from being deformed during assembling theinitiator. Connectors 23 a and 23 b shown in a chain line in FIG. 5 arefitted into and connected to the cavities 85. That is, the inside of thecavity 85 serves as a connecting portion in which the connector isfitted. A recessed notch 88 is provided inside the end portion of theconnector connecting cavity 85 of the metallic collar 40 in thecircumferential direction, thereby forming falling-out preventing meansfor the fitted connector.

When the center pin 54 a of the first igniter 32 a in the initiatorassembly 10 is electrified, the current flows through the grounding pin70 a via the bridge wire 19, the priming 62 is ignited and burnt in thecourse, and then the transfer charge 116 is ignited and burnt.Consequently, the seal tape 118 is ruptured by a high temperature gasgenerated by combustion of the transfer charge 116, the high temperaturegas enters the first combustion chamber 105 a through theflame-transferring holes 117, and the first gas generating agent 109 ais ignited and burnt to generate a gas.

In this case, when the priming 62 is ignited and burnt due to activationof the first igniter 32 a, the metallic pressing member 130 may bebroken by a pressure of that combustion and the broken portion may makea bridge between the first igniter 32 a and the second igniter 32 b. Insuch a situation, (+) current can flow in the second igniter 32 b viathe pressing member 130, or the pressing member 130 and the partitionmember 140.

Also, in a case that the metallic cover member 64 accommodating thepriming 62 in the first igniter 32 a makes contact with the pressingmember 130 to be electrified due to activation of the first igniter 32a, broken portions of the cover member 64 and the pressing member 130may make a bridge between the first igniter 32 a and the second igniter32 b. In such a situation, (+) current of the first igniter 32 a mayflow in the second igniter 32 b via the pressing member 130 or the like.At this time, even when an outer surface of the cover member 64 in bothigniters is covered with a film having an insulation (hereinafter,referred to as an insulating film), the same problem occurs when thefilm is broken.

Then, regarding the possibility such that (+) current of the firstigniter 32 a flows in the second igniter 32 b, even if the center pin inthe first igniter 32 a is set to (+) pole, a similar problem will occurwhen a tip end portion of the bridge wire connected to the center pin 54a makes contact with a conductive portion such as the cover member 64 orthe like, for any reason, after activation of the first igniter 32 a.

However, according to the present invention, if (+) current flows in thesecond igniter 32 b in this manner, the (+) current flows in only thegrounding pin 70 b, and never flows in the center pin 54 b.

Furthermore, when only the first igniter 32 a is activated, theopening-shutting means of current between the center pin 54 b of thesecond igniter 32 b and the external power supply is open so thatcurrent is prevented from flowing in the center pin 54 b. In a casewhere the opening-shutting means is shut or there is no opening-shuttingmeans, (+) current flows from the center pin 54 b to the grounding pin54 a of the first igniter 32 a through the bridge wire 19 and thebridging broken portion. In such a case, the priming 62 is ignited sothat the second igniter 32 b may be activated erroneously.

As mentioned above, in the present invention, since the center pin 54 bof the second igniter 32 b is set to the positive electrode and theopening-shutting means of current is provided between the center pin 54b and the external power supply, an erroneous activity of the secondigniter 112 b can be prevented unfailingly.

An air bag system according to the present invention can use thepyrotechnic type gas generators shown in FIG. 1 and FIG. 4. Moreover,any gas generator according to the present invention can be usedregardless of whether the gas generator is pyrotechnic or not. Forexample, when the gas generator for an air bag as shown in FIG. 1 isused, the air bag system may be provided with activation-signaloutputting means comprising an impact sensor and a control unit, and amodule case in which the gas generator and an air bag are accommodated.The gas generator is connected to the activation-signal outputting means(the impact sensor and the control unit) in the side where a firstigniter 117 and a second igniter 118 as shown in FIG. 6, are provided.Then, in the air bag system thus structured, by properly setting theactivation-signal outputting conditions in the activation-signaloutputting means, an inflation speed of the air bag can be adjusted inaccordance with a degree of an impact by activating only the firstigniter 117, or activating the first igniter 117 and the second igniter118 at different timings, or activating two igniters simultaneously.

More specifically, as shown in FIG. 6 which shows one embodiment of theair bag system of the present invention, the air bag system comprises agas generator 200, an impact sensor 201, a control unit 202, a modulecase 203, and an air bag 204. As the gas generator 200, the gasgenerator described with reference to FIG. 1 is used, and the activatingperformance thereof is adjusted to give as little an impact as possibleat the initial stage of activation of the gas generator.

The impact sensor 201 can comprise, for example, a semiconductor typeacceleration sensor. In this semiconductor type acceleration sensor,four semiconductor strain gauges are formed on a beam of a siliconsubstrate that bends when acceleration is applied, and thesesemiconductor strain gauges are bridge-connected. When an accelerationis applied, the beam deforms and strain is produced on a surface of thebeam. The resistances of the semiconductor strain gauges are changed dueto this strain, the resistance change is detected as a voltage signalproportional to the acceleration.

The control unit 202 is provided with an ignition-judgment circuit, anda signal from the semiconductor type acceleration sensor is inputted tothe ignition judgment circuit. The control unit 202 starts calculationat a time when the impact signal from the sensor 201 exceeds apredetermined value, and, when the calculated result exceeds apredetermined value, an activation-signal is outputted to the igniter ofthe gas generator 200, namely, the first igniter 117 or the secondigniter 11B.

The module case 203 is made of, for example, polyurethane and itincludes a module cover 205. The air bag 204 and the gas generator 200are accommodated in the module case 203 to be constituted as a padmodule. The pad module is ordinarily mounted to a steering wheel 207when it is mounted in a driver side in an automobile.

The air bag 204 is made of nylon (for example, nylon 66), polyester orthe like, the opening 206 thereof surrounds a gas discharging port ofthe gas generator, and the air bag is fixed to a flange portion of thegas generator in a folded state.

When the semiconductor type acceleration sensor 201 senses an impact ata time of collision of an automobile, the detection signal istransmitted to the control unit 202, and when the impact signal from thesensor exceeds the predetermined value, the control unit 202 startscalculation. When the calculated result exceeds the predetermined value,a working signal is output to the first igniter 117 or the secondigniter 118 of the gas generator 200. Thereby, the igniter is activatedto ignite the gas generating agent so that the gas generating agent isburnt to generate gas. This gas is injected to the air bag 204 andthereby the air bag breaks the module cover 205 to inflate such that acushion absorbing the impact is formed between the steering wheel 207and the occupant.

1. A gas generator for an air bag, comprising: a housing having a gasdischarging port; an initiator assembly provided with a first igniterand a second igniter mounted to the housing via a holder, each of thefirst igniter and the second igniter including a priming activated uponan impact, the second igniter having, a center pin connected to anexternal power supply to constitute a positive electrode, a groundingpin connected to a metal portion of a motor vehicle to constitute anegative electrode, and switch means of current provided between thecenter pin and the external power supply; and gas generating meansignited and burnt by the initiator assembly to generate a combustiongas.
 2. A gas generator for an air bag according to claim 1, wherein theinitiator assembly further includes, a transfer charge, wherein theholder is joined to the insulating material.
 3. A gas generator for anair bag according to claim 2, wherein, at least one of the first igniterand the second igniter includes, a metallic eyelet having a hole throughwhich one of the center pin and the grounding, and an electricalinsulating body for insulating the one of the center pin and thegrounding pin passing through the hole from the metallic eyelet, whereinan end surface of the one of the center pin and the grounding pin, asurface of the metallic eyelet, and a surface of the electricalinsulating body form a common plane.
 4. A gas generator for an air bagaccording to claim 1, 2 or 3, wherein the gas generator inflates anairbag solely by a combustion gas generated by combustion of the gasgenerating means.
 5. A gas generator for an air bag according to claim1, wherein the second igniter is activated simultaneously with the firstigniter or after an activation of the first igniter is activated.
 6. Agas generator for an air bag according to claim 1, wherein the groundingpin is electrically connected to a metal portion constituting an outershell vessel of the igniter, and the center pin is electricallyconnected to the grounding pin via only an electric resistance wire. 7.An air bag system, comprising: a gas generator for an air bag accordingto claim 1; an impact sensor for detecting an impact to activate the gasgenerator; an air bag having introduced therein a gas generated by thegas generator to inflate the air bag; and a module case accommodatingthe air bag.
 8. An air bag system, comprising: an air bag apparatusincluding, a gas generator for an air bag having a housing provided witha gas discharge port, and ignition means attached to the housing, and anactivation-signal outputting device for outputting an electricalactivation-signal to the gas generator, wherein, the ignition means isprovided with a first igniter and a second igniter activated by anelectrical activation-signal, and the first igniter and the secondigniter are mounted to the housing via a holder, each of the firstigniter and the second igniter includes a grounding pin electricallyconnected to a metal portion of an outer shell vessel of the igniter,and a center pin electrically connected to the grounding pin only via anelectric resistance wire and the metal portion, the activation-signaloutputting device is provided with a switch means for controlling theoutput of the activation-signal to each igniter, and in the secondigniter, the center pin is connected to the activation-signal outputtingmeans to serve as a positive electrode.
 9. A method of receiving anactivation-signal in a gas generator for an air bag activated byreceiving an electrical activation-signal, comprising: providing the gasgenerator having a gas discharging port formed in a housing thereof;providing ignition means including first and second igniters activatedby an electrical activation-signal; providing each of the first andsecond igniters with a grounding pin electrically connected to a metalportion of the igniter and a center pin electrically connected to thegrounding pin only via an electric resistance wire and the metalportion, the center pin of the second igniter serving as a positiveelectrode to receive the signal; and providing the ignition means in thegas generator.